Ammonium nitrate explosive and its production



United States Patent Ofiice 3,032,450 Patented May 1, 1962 ware NoDrawing. Filed Apr. 1, 1958, Ser. No. 725,480 19 Claims. (Cl. 149-7)This invention relates to an ammonium nitrate explosive and to itsproduction. In one of its aspects, the invention relates to theconversion of an ammonium nitrate fertilizer which has been clay-coatedand which is not readily detonatable to a readily detonatable explosiveby removing the clay coating and adding a combustible liquid. In anotherof its aspects, the invention relates to a method of converting such afertilizer grade ammonium nitrate as has been described in a manner asdescribed by heating and agitating together a combustible which isliquid under the conditions of operation and said ammonium nitrate untilthe clay-coating thereon has been substantially replaced with saidcombustible material. In another of its aspects, the invention providesan improved ammonium nitrate explosive by heating the combustible-coatednitrate to a temperature at which the nitrate passes through a phasetransition which causes cracking of the nitrate and allows the oil tosoak into the individual particles thereof.

The conventional clay-coated ammonium nitrate which is the ordinarycommercial product used for fertilizer is not readily detonatable andwhen mixed with the proper amount of combustible material, such aspetroleum hydrocarbon, which is used in the preparation of detonatableammonium nitrate, the said commercial product produces a ratherdifficulty detonatable material.

Explosives with ammonium nitrate as the oxidizer are old in the art. Theammonium nitrate is intimately mixed with or soaked with a combustiblematerial such as peat, petroleum distillates or residues, coke, andsimilar materials. It has been established that detonationcharacteristics are favorably affected by low moisture content of theammonium nitrate, this ordinarily being below 1.5 weight percent, and byintimate contact between the ammonium nitrate and the combustiblematerial.

It is known that there are a number of variables which afiect the easeof detonation of ammonium nitrate explosives. Included among thesevariables, which are known to one skilled in the art of ammoniumexplosives, are the following which are applicable to ammonium nitrateand mineral oil mixtures: fineness of ammonium nitrate; fineness ofcombustible, when it is a solid at ordinary temperatures; 'diiferencesin the method of coating the ammonium nitrate with the combustible;differences in the specific types of combustible materials used;variation of the moisture content.

The ready and general availability of fertilizer grade ammonium nitratemakes it desirable as a material for use in explosives. However, asnoted, the clay-coated commercial product is unsuited for explosivepurposes.

I have now found that if the conventional clay-coated ammonium nitratefertilizer is agitated with a petroleum hydrocarbon, such as a gas oilor diesel fuel, until the clay coating has been removed from the nitrateparticles and the oil coated thereon, that the ammonium nitrate which isthus freed of the clay coating and soaked with the liquid hydrocarbonhas good detonating properties.

It is an object of this invention to provide an ammonium nitrateexplosive. It is another object of this invention to provide a methodfor the preparation of an ammonium nitrate explosive. It is a furtherobject of the invention to provide a method for producing an ammoniumnitrate explosive from a fertilizer grade ammonium nihydrocarbons beingfound in the exit sweep gas.

trate. A still further object of the invention is to produce acombustible-coated ammonium nitrate particle. A further object still isthe production of a combustiblecoated ammonium nitrate particle in whichthe coating is, at least in part, found within cracks in the surfaces ofthe particle.

Other aspects, objects and several advantages of the invention areapparent from this description and the claims.

According to the present invention, there is provided a method for thepreparation of a detonatable ammonium nitrate composition from a coatedammonium nitrate product unsuitable for use as an explosive because ofits poor detonatability which comprises intimately contacting saidcoated ammonium nitrate with a combustible which is liquid under thetreating conditions for a time and in a manner so as to remove thecoating from the ammonium nitrate and to coat the same with saidcombustible, and recovering said combustible-coated ammonium nitratefrom the treating mass.

Thus, the process of the present invention comprises the steps ofremoving the clay coating from the ammonium nitrate and forming anexplosive composition of uncoated ammonium nitrate which is soaked witha combustible which is liquid under the treating conditions and suchthat it will not hinder the detonation of the final product of theinvention, the combustible being usually a petroleum hydrocarbon such asdiesel oil, gas oil, etc. The process can be practiced readily byforming, for example, in a jet-agitated vessel, a slurry of coatedammonium nitrate prills with diesel fuels or oils, such as a gas oil,the moving hydrocarbon removing the clay from the prills and forming asuspension of the clay in the hydrocarbon. The clay is removed bydraining the excess hydrocarbon and suspended clay from the prills. Thisis accomplished in a batch operation by draining off the excess liquidhydrocarbon and suspended clay. Continuous operation is within the scopeof the invention and can be practiced by providing an agitating zoneadjacent a conveyor zone, the coated prills being fed to the agitationzone for agitation with the oil and passed through the conveying zonewherein the prills are allowed to settle and the supernatant oil layeris decanted. The prills are allowed to drain until the oil-soaked prillsare about five to ten percent by weight oil and the remainder, ammoniumnitrate. The explosive composition is then ready for use. Agitation isordinarily discontinued while draining away the hydrocarbon containingthe suspended clay. However, some agitation, at least of the hydrocarbonphase, can be provided to insure good suspension of the clay therein, inthe event some settling of the clay which is, in the specific instance,undesirable, is occurring. Ordinarily, some clay in the final product,not usually more than that suspended in the oil coating, will not beobjectionable. Indeed, the final product appears to be quite suitablewhen it contains some clay.

Also, according to the present invention, there is provided theimportant and now preferred feature of drying the ammonium nitrateduring the removal of the clay coating therefrom for some timethereafter. This is accomplished by heating the oil-ammonium nitratemixture preferably with agitation and preferably providing for theremoval of vaporized water with an entrainer gas, for example, in asweep stream of natural gas. The liquid hydrocarbon used in thismodification is preferably a low volatility fraction such as describedsince this facilitates operation without high concentration of vapors ofliquid Otherwise, more volatile combustible materials can be used whichwould be those known in the art. The liquid hydrocarbon or othercombustible material, if desired, can contain particles of carbon blackor other materials which are found to preferentially deposit with thecombustible on the nitrate particle.

When heating is practiced according to the invention, it is practicedfor, at least, one of several reasons.

One reason for heating the oil-coated prills is to pass the prillsthrough a phase transition point which occurs at about 90 F. Suchheating is useful even though no substantial dehydration is practiced.Thus, the passing through a phase transistion point at about 90 F.causes a rather large volume change to take place which aids in crackingthe prills and allowing the oil to enter them more readily. This is alsoadvantageous in the formation of a uniform mixture and in contactingintimately the oil and the nitrate.

Another reason for heating is, of course, the dehydration of the finalproduct to bring it within the desired known low water content iimit.The heating can be accomplished at any time during the operation, forexample, during agitation or thereafter. When heating is practiced, itis practiced to increase substantially the vapor pressure of the waterand preferably, the temperature will be at or above the boiling point ofwater, for example, in a range of from about 210 to about 225 F. Theheating time usually is in the range of live minutes to two hours, moreusually in the range from about ten minutes to one-half hour. The excessoil, if any is prescut when heating occurs, is drained and the oil orcombustible material coated prills cooled, thus yielding a compositionready for use in blasting.

The blasting compositions formed by the process of this invention can beused in a conventional and known manner, they can be packed in bags orother containers for placing in the hole, and, for use in wet locations,the containers are preferably water-proof. These containers can be, forexample, paper, cloth or plastics such as polyethylene.

Example I Prilled uncoated ammonium nitrate as used in the preparationof coated ammonium nitrate of fertilizer grade and having an averageparticle size of 14 mesh was soaked with 7 weight percent diesel fueland then detonated in cardboard tubes with Primacord as an initiator. Asimilar mixture made with clay-coated ammonium nitrate prills would notdetonate under the same conditions. indeed, it would not detonatewhen'dynamite booster was used. Several mixtures of the uncoatedammonium nitrate soaked with 7 Weight percent diesel fuel and several ofthe similar mixtures with clay-coated ammonium nitrate prills whichwould not detonate, were prepared to confirm the first-reported findingsof this example.

Example If A mixture of coated ammonium nitrate of fertilizer grade anddiesel fuel and a mixture of uncoated ammonium nitrate and diesel fuelwere prepared and detonated confined in an iron pipe. The initiatorswere dynamite boosters set off with a small amount of Primacord.(Samples confined in an iron pipe can be detonated in certain instanceswhere the lower degree of confinement of a cardboad tube will not resultin detonation.) The uncoated ammonium nitrate and diesel fuel mixturedetonated with 54 plastic cards between the initiator and the explosive.The clay-coated ammonium nitrate-diesel fuel mixture detonated with amaximum of 12 cards between the initiator and the explosive. Several ofeach of the mixtures were prepared to confirm the findings reported inthis example.

Petroleum hydrocarbons particularly suited for use in this invention arethose boiling in the range of 250 F. to 800 F., preferably from about300 F. to 700 F. These ranges include distillates known in the petroleumrefining art as kerosene, gas oil, diesel fuel, stove oil, and numerousothers.

The ammonium nitrate is at least for the most part available as prillswithin the range of 10 to 20 mesh in size. Some of the fertilizer isavailable as crystallized ammonium nitrate, and a small part isavailable as a ground product. These latter products may contain aconsiderable amount of particles finer than 20 mesh and as fine as mesh.

The clay coating on the ammonium nitrate is usually diatomaceous earth,although a relatively minor portion of the fertilizer is coated withkaolin, fullers earth or other clays. The amount used varies to someextent, but 3 /2 percent (based on the total) is a representativeamount.

Reasonable variation and modification are possible within the scope ofthe foregoing disclosure and the appended claims to the invention, theessence of which is that a fertilizer grade clay-coated ammonium nitrateis rendered suitable for use as an explosive by replacing theclay-coating of the ammonium nitrate with a combustible material such asa hydrocarbon, substantially as set forth and described herein.

I claim:

1. A method for the conversion of a clay-coated fertilizer gradeammonium nitrate to an explosive which comprises admixing said ammoniumnitrate with a liquid petroleum hydrocarbon, agitating the mixture untilsubstantially the entire clay coating has been removed from theparticles of the ammonium nitrate and the particles have been coatedwith the liquid petroleum hydrocarbon, removing any liquid in excess ofthat wetting the particles, and recovering an explosive liquid-coatedammonium nitrate.

2. A method according to claim 1 wherein said liquid petroleumhydrocarbon has a boiling point in the range of about 250 F. to about800 F.

3. A method according to claim 2 wherein the excess liquid is removeduntil the liquid-coated ammonium nitrate particles are in the range ofabout 5 to about 10 weight percent liquid petroleum hydrocarbon.

4. A method according to claim 3 wherein the liquidcoated ammoniumnitrate particles are heated to pass the ammonium nitrate through aphase transition which occurs at about F.

5. A liquid petroleum hydrocarbon ammonium nitrate explosive preparedaccording to the method of claim 4.

6. A method for the conversion of a clay-coated fertilizer gradeammonium nitrate to an explosive which comprises admixing said ammoniumnitrate with a liquid petroleum hydrocarbon, agitating the mixture untilsubstantially the entire clay coating has been removed from theparticles of the ammonium nitrate and the particles have been coatedwith the liquid petroleum hydrocarbon, removing any liquid in excess ofthat wetting the particles, and heating the liquid-coated ammoniumnitrate particles to pass the ammonium nitrate through a phasetransition.

7. A liquid petroleum hydrocarbon ammonium nitrate explosive preparedaccording to the method of claim 6.

8. A method for the preparation of an explosive composition whichcomprises intimately contacting ammonium nitrate particles with a liquidpetroleum hydrocarbon and heating the thus-formed mixture at least to atemperature at which the ammonium nitrate passes through a phasetransition, thereby producing cracks in the surfaces of the ammoniumnitrate particles, the cracks being, at least in part, filled with saidliquid petroleum hydrocarbon.

9. A method for the preparation of an explosive composition whichcomprises intimately contacting ammonium nitrate particles with a liquidpetroleum hydrocarbon and heating the thus-formed mixture to pass theammonium nitrate through a phase transition which occurs at about 90 F.

10. An explosive composition prepared according to claim 8.

11. An explosive composition prepared according to claim 9.

12. A method according to claim 1 wherein during the removal of thecoating, said ammonium nitrate and said liquid petroleum hydrocarbon areheated and an entrainer gas is passed through the mass to facilitateremoval of water from said ammonium nitrate.

13. A method according to claim 1 wherein the mixture is heated duringagitation.

14. A method according to claim 1 wherein the mixture is heated to atemperature in the range of approximately 210-225 F.

15. A method according to claim 1 wherein said liquid petroleumhydrocarbon is diesel fuel.

16. A method according to claim 1 wherein said liquid petroleumhydrocarbon is gas oil.

17. A method according to claim 1 wherein an entrainer gas is passedthrough the mixture during said step of agitating.

18. A method according to claim 17 wherein the entrainer gas is naturalgas.

19. A method for the conversion of a clay coated fer- References Citedin the file of this patent UNITED STATES PATENTS OBrien Sept. 2, 1913Kirst et al Feb. 26, 1935 Taylor et a1 Mar. 18, 1952 OTHER REFERENCESPerry: Chemical Engineers Handbook, 3rd Edition,

20 3rd Impression, 1950, p. 1118.

Daugherty: Chemical and Engineering News, October 7, 1957, pp. 62 and63, 52-05 S & L.

1. A METHOD FOR THE CONVERSION OF A CLAY-COATED FERTILIZER GRADEAMMONIUM NITRATE TO AN EXPLOSIVE WHICH COMPRISES ADMIXING SAID AMMONIUMNITRATE WITH A LIQUID PETROLEUM HYDROCARBON, AGITATING THE MIXTURE UNTILSUBSTANTIALLY THE ENTIRE CLAY COATING HAS BEEN REMOVED FROM THEPARTICLES OF THE AMMONIUM NITRATE AND THE PARTICLES HAVE BEEN COATEDWITH THE LIQUID PETROLEUM HYDROCARBON, REMOVING ANY LIQUID IN EXCESS OFTHAT WETTING THE PARTICLES, AND RECOVERING AN EXPLOSIVE LIQUID-COATEDAMMONIUM NITRATE.